1. Field of the Invention
The present invention relates to cogeneration with effective utilization of thermal and electrical energy. More particularly, this invention is concerned with utilization of cogenerated electrical energy in residential, commercial and possibly industrial applications each having multiple service loads wherein individual electrical service loads are switched between utility grid and cogeneration sources by solid state switching controlling the electrical demand on the cogeneration source.
2. Description of Prior Art
Solid state load switches which operate at the time the voltage waveform passes through zero and zero crossing detectors are known to the art, as exemplified by U.S. Pat. Nos. 5,070,251; 4,879,624; 4,703,191; 4,427,897; and 3,665,212. U.S. Pat. No. 5,012,121 teaches a solid state under voltage switch to supply high amounts of electrical energy for brief periods, 100 ms, from a capacitor to a load. U.S. Pat. No. 4,262,212 teaches a control circuit responsive to load demands for transfer of power supplied to a recreational vehicle between land line, motor generator and invertor.
Auxiliary and standby power generators and methods of their operation, control and switching is taught by a wide variety of patents of which the following are exemplary. Computer controlled synchronization and switching of standby battery sources for replacement of power in AC line upon failure is taught by U.S. Pat. No. 5,070,251. U.S. Pat. No. 4,916,329 teaches an uninterruptible power supply having a series of regulator switches to maintain load output voltage within limits during variations in AC input voltage by supply of power through a transformer. A plurality of generators for operation under peak loads of a primary and secondary load system while a single generator operates under low load conditions when the secondary load system is switched off is taught by U.S. Pat. No. 2,655,602. U.S. Pat. No. 1,714,938 teaches two generators, the second operable upon need demand and switching equipment therefore. Auxiliary power generators to reduce peak electrical demand on an electrical distribution network by operating at a preset demand point with at least one secondary generator in parallel with the electric utility system is taught by U.S. Pat. No. 4,731,547. Solar cell operation of a DC motor to drive an AC motor-generator to reduce power drawn from and to return power to an AC utility line is taught by U.S. Pat. No. 4,131,827.
Generation of electrical power by windmills wherein the generated power is a function of the wind velocity is generally known. To match the electrical load to the wind generator, U.S. Pat. No. 4,205,235 teaches switching five different loads to a wind generator output, each load corresponding to a range of speeds of the wind driven generator's rotor. U.S. Pat. No. 4,511,807 teaches maintenance of relatively constant electrical output frequency of a wind generator with changes in wind velocity by sensing frequency of the output and switching the load by solid state zero crossing relays between domestic resistive heaters and dump resistors which act as a governor, tending to limit the maximum speed of rotation of the wind turbine.
Residential cogeneration units utilizing thermal and electrical output are exemplified by the following references. U.S. Pat. No. 4,262,209 teaches an internal combustion engine driving an externally excited commutator AC motor-generator to provide AC power at a magnitude which is a function of the drive shaft velocity and degree of excitation to provide supplemental power to meet load requirements with engine heat being used for household uses. Residential cogeneration using peak time statistical analysis to predetermine transfer of a single household electrical load from an electric utility source to the cogeneration source by a single transfer switch is taught by U.S. Pat. No. 3,678,284. U.S. Pat. No. 4,752,697 teaches a cogeneration system having a plurality of cogenerators in which one unit is varied to regulate output and others are full on or full off to provide desired electrical output. Microprocessor-based control of cogeneration systems by selection of thermal or electrical load following modes and tailoring for economic considerations, performance characteristics, and cogenerator operating constraints providing electrical power which may be switched between a single load or the power grid is taught by U.S. Pat. No. 4,802,100. U.S. Pat. No. 4,510,756 teaches cogeneration controlled by a signal from the utility for supplying electricity to a residential service box and having centralized high and low grade heat storage for supply to multiple residences. The utilization of cogeneration systems in parallel with the utility grid to feed excess electricity into the utility grid is taught by the following U.S. Patents. U.S. Pat. No. 4,715,192 teaches an open cycle air conditioning unit in combination with a cogenerator which is thermally or electrically controlled based upon the need of the entire facility. U.S. Pat. No. 4,686,375 teaches a cogeneration system having two electrically isolated generators connected to a common shaft, one for supply to a facility for electrical consumption and a second for supply to a utility grid. U.S. Pat. No. 4,438,340 teaches a domestic cogenerator which feeds power into an entire building and when voltage output reaches 220 volts disconnects or feeds excess power into the utility grid.